One of the object yōkai illustrated in the Hyakki Tsurezure Bukuro. Its name contains two puns, the first being the homophonic relationship between the oroshi in its name, which refers to wind blowing from the mountains, and the oroshi (下ろし), or vegetable grater, of which it appears to be a transformation. The second is revealed in Sekien's poetic explanation:

豪猪（がうちょ）といへる獣あり。 山おやじと言ひて、そう身の毛はりめぐらし、此妖怪も名とかたちの似たるゆへにかく言ふならんと、夢心におもひぬ。
There is a beast called gaucho (gōcho). It is [also] called yama-oyaji, and indeed hair-spines surround its body, and this yōkai also resembles its name in form, so it must not be said, and I saw it not in the heart of a dream.

The gōcho refers to the yama-arashi, a spiny creature described in the Wakan Sansai Zue which lives in groups deep in the mountains and shoots its foot-long quills like arrows when it is angry. This seems to be a fanciful description of the zoological porcupine, which today is called yama-arashi in Japanese.

Sekien seems to made a play on the name yama-arashi to get yama-oroshi, having seen the potential for a spiny, porcupine-like creature in the toothy serrations of a grater.

Citations
1. Murakami 2000 p. 344-6, Inada p. 320.